most likely your gpus memory cant support those speeds try lowering the memory speed to 6950s default 1250 and see what happens if that dosent work then just flip the damn switch for the backup bios and presto your back to 6950 regular performance and just overclock the friggin thing as overclocked via catalyst the 6950 matches a stock 6970

if the second screen of GPU-Z is true than ur card ain't running full speed only x1 and not x16 maybe try take the card out, reset ur bios on the motherboard, plug the card back in remember power and turn on the machine ^^;